Probing Charge Transport at the Single-Molecule Level on Silicon by Using Cryogenic Ultra-High Vacuum Scanning Tunneling Microscopy
A cryogenic variable-temperature ultra-high vacuum scanning tunneling microscope is used for measuring the electrical properties of isolated cyclopentene molecules adsorbed to the degenerately p-type Si(100)-2×1 surface at a temperature of 80 K. Current-voltage curves taken under these conditions sh...
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Published in | Proceedings of the National Academy of Sciences - PNAS Vol. 102; no. 25; pp. 8838 - 8843 |
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Main Authors | , , , |
Format | Journal Article |
Language | English |
Published |
United States
National Academy of Sciences
21.06.2005
National Acad Sciences |
Series | Molecular Electronics Special Feature |
Subjects | |
Online Access | Get full text |
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Summary: | A cryogenic variable-temperature ultra-high vacuum scanning tunneling microscope is used for measuring the electrical properties of isolated cyclopentene molecules adsorbed to the degenerately p-type Si(100)-2×1 surface at a temperature of 80 K. Current-voltage curves taken under these conditions show negative differential resistance at positive sample bias, in agreement with previous observations at room temperature. Because of the enhanced stability of the scanning tunneling microscope at cryogenic temperatures, repeated measurements can be routinely taken over the same molecule. Taking advantage of this improved stability, we show that current-voltage curves on isolated cyclopentene molecules are reproducible and possess negligible hysteresis for a given tip-molecule distance. On the other hand, subsequent measurements with variable tip position show that the negative differential resistance voltage increases with increasing tip-molecule distance. By using a one-dimensional capacitive equivalent circuit and a resonant tunneling model, this behavior can be quantitatively explained, thus providing insight into the electrostatic potential distribution across a semiconductor-molecule-vacuum-metal tunnel junction. This model also provides a quantitative estimate for the alignment of the highest occupied molecular orbital of cyclopentene with respect to the Fermi level of the silicon substrate, thus suggesting that this experimental approach can be used for performing chemical spectroscopy at the single-molecule level on semiconductor surfaces. Overall, these results serve as the basis for a series of design rules that can be applied to silicon-based molecular electronic devices. |
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Bibliography: | ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 This paper was submitted directly (Track II) to the PNAS office. Edited by Mark A. Ratner, Northwestern University, Evanston, IL, and approved May 12, 2005 To whom correspondence should be addressed. E-mail: m-hersam@northwestern.edu. Author contributions: N.P.G., N.L.Y., and M.C.H. designed research; N.P.G. and N.L.Y. performed research; N.P.G., N.L.Y., and M.C.H. analyzed data; and N.P.G. and M.C.H. wrote the paper. Abbreviations: UHV, ultra-high vacuum; STM, scanning tunneling microscope; NDR, negative differential resistance; HOMO, highest occupied molecular orbital. |
ISSN: | 0027-8424 1091-6490 |
DOI: | 10.1073/pnas.0501214102 |